Azo dyes are those to be formed by azo-coupling of so-called coupler components such as active hydrogen-containing compounds, phenols and p-dialkylaminobenzenes and a so-called diazo component of diazonium salts prepared from aminoaryl compounds or aminoheteroaromatic compounds. Since azo dyes are composed of selected coupler components and azo components of various structures, they have various tones and are typical components of dyes.
Of them, known are aminopyrazole azo dyes, pyridone azo dyes and diaminopyridine azo dyes as those having a heterocyclic coupler component.
Recently, color electronic photography, ink jet system color duplication, thermal transfer system color duplication, printing ink, and diffusion transfer system silver salt photography have become studied actively, and azo dyes are used as image forming dyes in them.
On the other hand, demand for filters for solid television camera tubes and color liquid crystal television is increasing with development of electroimaging, and azo dyes have become studied also as dyes for filters.
However, known azo dyes have various problems that need to be solved. For instance, the absorption of the dyes is not sufficiently sharp, thereby causing problems of the color reproducibility of the images from them and the capacity of filters containing them.
In addition, the dyes do not have sufficient fastness to light, heat, air, moisture and chemicals, which thereby causes problems of the storage stability of images from them and the durability of filters containing them.
Further, where the dyes are used for thermal transfer, the transferability of the dyes is not sufficient.
In addition, production of the dyes is difficult and the cost of the dyes is high.
In order to solve the above-mentioned problems, the present inventors earnestly studied azo dyes having a coupler component of imidazoles. As a result, they have found that imidazole azo dyes have sharp absorption, have high fastness to light, heat, air, moisture and chemicals and have high thermal transferability.
In addition, they have also found that when imidazole azo dyes are incorporated into thermal transfer dye-donating materials along with aminopyrazole azo dyes, the storage stability of the materials as well as the storage stability of images transferred on an image-receiving layer from them is extremely improved. On the basis of these findings, the present invention has been completed.
The related conventional knowledge is described below.
J. Chem. Soc., Perkin Trans. II (12), pages 2055-2058 has a description relating to the reactivity of imidazoles and diazonium salts. However, this bears no relation to the present invention. This has no description relating to dyes to be formed by reaction of imidazoles and diazonium salts.
DE-2129524 has a description referring to 2-alkyl-4-phenylazo-4H-imidazoles. However, this also bears no relation to the present invention. This merely mentions that imidazole azo compounds can be used as a microbicide and is silent on dyes.